In many bird species, ovarian activity and ovulation occur when a female interacts with a male. This neuroendocrine response occurs even when physical contact between male and female is prevented. Recent evidence from ring doves, Streptopelia risoria, suggests that the increased ovarian activity is stimulated most directly by the female's own vocal behavior which she performs in response to the courting behavior of the male. Incidental observations indicate that ovulation and egglaying also occur when a female is sexually imprinted upon her human keeper, suggesting that neuroendocrine responses, like overt behavioral responses, are shifted in the imprinting process. Much less is known about the neuroendocrine responses of males. Three studies clearly show that plasma testosterone levels rise markedly shortly after a male is placed with a female, but the following questions--to be addressed in the research proposed here--remain unanswered. 1. Is the rise in plasma testosterone stimulated by the male's own vocal behavior as he courts the female? 2. Is the rise in testosterone primarily attributable to increased activity in the left testis? (Preliminary evidence from our laboratory indicates that the left testis is relatively inactive in socially isolated male doves but that it equals the right testis in activity after the male is introduced to a female). 3. Does an increase in plasma testosterone occur when the male dove is introduced to a human keeper or another species upon which he has been sexually imprinted? Affirmative answers to these questions will have important implications. For example, recent evidence indicates that the immune system is heavily influenced by gonadal steroids such as testosterone. If we show that testosterone secretion is influenced by self-feedback from overt behavior, we shall have a model system for examining how an individual's own behavior can affect his resistance to pathogens. Second, if we show that neuroendocrine responses are affected by sexual imprinting, it may suggest that psychosexual orientation involves more of the total organism than is commonly recognized. Finally, if we confirm our observation of an asymmetrical testicular response, it may show that the two testes in doves do not simply duplicate each other's activity but are performing different functions.